#include <stdio.h>

int main(void)
{
    int urn[5] = {100, 200, 300, 400, 500};
    int *ptr1, *ptr2, *ptr3;
    ptr1 = urn; // 把一个地址赋给指针
    ptr2 = &urn[2]; // 把一个地址赋给指针
    // 解引用指针，以及获得指针的地址
    printf("pointer value, dereferenced pointer, pointer address:\n");
    printf("ptr1 = %p, *ptr1 =%d, &ptr1 = %p\n", ptr1, *ptr1, &ptr1);

    // 指针加法
    ptr3 = ptr1 + 4;
    printf("\nadding an int to a pointer:\n");
    printf("ptr1 + 4 = %p, *(ptr1 + 4) = %d\n", ptr1 + 4, *(ptr1 + 4));

    ptr1++; // 递增指针
    printf("\nvalues after ptr1++:\n");
    printf("ptr1 = %p, *ptr1 =%d, &ptr1 = %p\n", ptr1, *ptr1, &ptr1);

    ptr2--; // 递减指针
    printf("\nvalues after --ptr2:\n");
    printf("ptr2 = %p, *ptr2 = %d, &ptr2 = %p\n", ptr2, *ptr2, &ptr2);

    --ptr1; // 恢复为初始值
    ++ptr2; // 恢复为初始值
    printf("\nPointers reset to original values:\n");
    printf("ptr1 = %p, ptr2 = %p\n", ptr1, ptr2);

    // 一个指针减去另一个指针
    printf("\nsubtracting one pointer from another:\n");
    printf("ptr2 = %p, ptr1 = %p, ptr2 - ptr1 = %td\n", ptr2, ptr1, ptr2 - ptr1);

    // 一个指针减去一个整数
    printf("\nsubtracting an int from a pointer:\n");
    printf("ptr3 = %p, ptr3 - 2 = %p\n", ptr3, ptr3 - 2);

    return 0;
}
